The EPA Groundwater Protection Strategy has established differential protection levels based on the beneficial uses of groundwaters. Groundwater resources that are: (1) Irreplaceable sources of drinking water; and/or (2) Ecologically Vital are designated as of unusually high value. To determine those groundwaters that meet the EPA criteria for qualifying as "Ecologically Vital" we have examined 63 groundwater based (wetland) ecological systems on the island of O'ahu. An inventory of the physical, biological and cultural characteristics of each area including certain "red flag" features has been developed and coded. Using this "habitat code" a rating system that reflects the sensitivity, i.e. "uniqueness" or "nonrenewable" attributes of each system was designed and 46 "ecologically vital" habitats were identified that meet the EPA criteria for Class 1 level of groundwater protection.